This invention relates to a process of producing copolymers, and more particularly to a process of producing styrene-based copolymers having excellent transparency and thermal resistance which is capable of performing bulk continuous polymerization having excellent manufacturing efficiency in an industrially advantageous manner.
In general, as styrene-based resin having excellent thermal resistance, styrene-maleic anhydride copolymers have been known.
However, a copolymerization reaction of the aromatic vinyl compound such as styrene and maleic anhydride tends to produce an alternate copolymer since the reactivity of the maleic anhydride is high. Therefore, it has been impossible in ordinary processes to produce the uniform and useful copolymer in which the content of maleic anhydride unit is controlled within a specified range.
For this reason, as processes of producing such useful copolymer, (1) a process of performing copolymerization of styrene and maleic anhydride by bulk polymerization to the extent of 5 to 40% of styrene to complete copolymerization substantially, and performing polymerization of styrene remaining by suspension polymerization (Japanese Patent Publication No. 19914/1979), and (2) a process of adding methyl methacrylate as a third ingredient when the styrene and maleic anhydride are copolymerized (Japanese Patent Laid-open Publication No. 102614/1980) have been known.
However, in the foregoing process (1), the product becomes a mixture of the copolymer having extremely high content of the maleic anhydride which is obtained by the bulk polymerization and a styrene homopolymer which is obtained by the suspension polymerization. Therefore, the above process (1) has defects that the copolymer produced has low thermal resistance and inferior transparency, and that the copolymer becomes heterogeneous since it is precipitated in the bulk polymerization. On the other hand, in the foregoing method (2), since the methyl methacrylate is indispensable as the third ingredient, it is impossible to obtain the styrene-maleic anhydride copolymer and copolymer obtained is different therefrom.